Adult Pacific lamprey (Lampetra tridentata Gairdner) encounter up to nine mainstem hydropower dams during their pre-spawning migration in the Columbia River Basin, USA. Radiotelemetry studies indicate that lamprey passage efficiency (the proportion that pass at each dam) is low relative to that of adult salmonids. In addition, lamprey migration is often delayed for over 5 days as they negotiate fishways designed to facilitate salmonid passage. We applied ‘time-to-event’ analyses (here, time to passage) to 4 years of lamprey passage data by setting the ‘hazard rate’ of traditional epidemiological studies equal to passage rate. Lamprey passage rates varied as a function of time, along with time-varying predictor variables (such as water temperature, river flow and spill). We used the Akaike Information Criterion to compare several competing versions of the model (each using a different predictor variable). Thus, we were able to distinguish the relative contribution of various factors to migrational delay. By fitting the model with a log-likelihood function, we incorporated information from individual fish rather than aggregated groups of fish. Consequently, this method is able to derive more information from small data sets than more traditional approaches. Moreover, models of this kind allow examination of multiple functional relationships to better explain patterns of fish behaviour obtained from fish telemetry programs. 61 Spedicato, M.T.; Lembo, G.; Marmulla, G. (eds.) Aquatic telemetry: advances and applications. Proceedings of the Fifth Conference on Fish Telemetry held in Europe. Ustica, Italy, 9-13 June 2003. Rome, FAO/COISPA. 2005. 295p.
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